Rail cars have been used for many years to efficiently haul large quantities of bulk materials over land. Items commonly shipped include grain, iron ore and coal. Shipping such items via rail car is very efficient due to the ability to transport extremely large loads of these materials in one shipment. For example, one single rail car may hold up to 110 tons of coal and an entire train made up of such cars may be over 130 cars in length, extending 6000 feet in total length.
Once at the destination, it is necessary to unload the cargo. For bulk material such as grain, ore, or coal, bottom-dumping and rotary-dumping are commonly used. Bottom-dumping involves staging a particular car over a receiving pit and opening hatches located in the bottom of the car. The cargo exits the car though the bottom hatches or doors and proceeds into the pit below. U.S. Pat. No. 5,302,071, assigned to Svedala Industries, Inc., discloses one example of a bottom-dumping rail car.
Bottom-dumping requires the use of rail cars that are specifically designed for bottom-dumping. This is due to the need to direct the car contents to a centrally located chute on the bottom of the car. The sides of the car must be at least partially sloped to urge the contents towards the chute, or else there would be a partial retention of the material being carried. This configuration decreases the ratio of the car's size vs. cargo capacity. Additionally, the bottom-dump configured rail cars are not easily interchangeable with standard cars at a dumpsite because the dump apparatus for standard cars must be uniquely configured to accommodate bottom-dump cars. The bottom-dump rail cars are also environmentally disadvantageous, as will be described more fully below.
Rotary-dumping is the other commonly used method of unloading a rail car. In rotary-dumping, a standard rectangular rail car is staged or indexed in a rotary-dump apparatus. The apparatus then rotates approximately one-half turn, thereby dumping the contents of the car into a receiving pit. Typically, the cars of the train remain connected during the dumping process through the use of rotary couplings between each car. Such couplings permit the cars to be rotated while still connected though an axis center at the coupling. U.S. Pat. Nos. 4,479,749 and 4,609,321, both assigned to Dravo Corporation, disclose conventional rotary-dump apparatuses. In some applications, such as the dumping of coal at major power plants, cars may be rotated and emptied at the rate of one car every four minutes.
Environmental pollution is an important concern to the design of a material dumping facility. When the car's load is dumped, a large quantity of material exits the car in a very short time. The turbulence generated by the quick unloading causes fine dust particles to billow up from the receiving pit and pollute the air surrounding the dump facility. The resulting dust, such as from grain or coal, is very explosive when in sufficient density. It is also an environmental pollutant. Therefore, there is a need to provide an apparatus and method for minimizing the polluting effect of dust.
Bottom-dump apparatuses have two critical drawbacks. First, they require special cars equipped with the bottom chutes as discussed previously. Second, the dust cloud produced by bottom-dumping is recognized by those skilled in the art to be larger, more aggressive and less controllable than the cloud produced by the rotary-dump method.
Rotary-dump systems control the dust cloud by using fans with large motors to exhaust the dust-filled air surrounding the car though conduits and into filtering devices. This process requires a very high flow of air and correspondingly very large motors to drive such high capacity system. These motors are commonly several hundred horsepower. Multiple motors of this size may be required at any given installation.
The cloud is typically large enough and aggressive enough to overpower any given removal system. Therefore, the airflow around the car and in the pit is controllably designed to keep the dust cloud suppressed long enough to allow the dust collection system to suck the dust from the surrounding area. The better the airflow is managed, the less horsepower is needed to drive the system. This results in greatly improved efficiency.
The Dravo patents listed above disclose a method of enclosing a rail car within a fixed enclosure. This design has several drawbacks. First, it restricts the operator's ability to observe the load as it is being dumped to ensure that the system does not malfunction and that no impurities or foreign objects are introduced into the pit. Next, the fixed enclosure requires multiple large motors to drive the plurality of air handling units. The filtering portions of the air handling units are within the dumping facility, which makes cleaning and maintenance more difficult. The presence of the air filtering units in the dumping facility exposes the facility to the risk of damage due to the force of explosions that sometimes occur in the filtering assemblies. Finally the efficiency of the system is low due to the large motors required to produce sufficient air removal capacity because the control of the airflow around the car does not have good dust cloud retention time.
Therefore, there is a continuing need to provide a rotary-dumper dust collection apparatus and system that overcomes the drawbacks of the prior art.